In rectangular balers, bales are formed by compressing crop material in a bale chamber by a plunger that reciprocates in the bale chamber. The bale chamber typically comprises a top wall, a bottom wall, and two side walls. At one end of the bale chamber there is provided a plunger. The plunger is typically guided in the bale chamber using a plurality of guide rollers and corresponding guide tracks.
An example of a guide system with a plurality of horizontal and vertical rollers and corresponding tracks is disclosed in U.S. Pat. No. 3,059,569 in the name of the Applicant. The vertical rollers, i.e. the rollers with a vertical axis may be adjustable. Each vertical roller is carried on a vertical stud which passes through an elongated slot in a bracket of the plunger. The elongated slot extends in a direction transverse to the bale chamber, and provides a means whereby the roller can be adjusted toward and away from a track member. A problem with such a guide system is that due to the high forces exerted on the vertical rollers during a compression stroke, the studs carrying the vertical rollers may be pushed inward in the elongated slot, resulting in misalignment and damage of the guide system.
Another example of a guide system is disclosed in GB 1,161,650. This guide system uses a plurality of guide rollers having an axis making an angle of 45 degrees with respect to a horizontal plane. The guide tracks are arranged in the corners, along the longitudinal edges of the bale chamber. Also in such an embodiment the reaction forces exerted on the rollers during the compression stroke may be high and may lead to problems.